At present, self-service terminal devices having an embedded printing device have been widely applied in everyday life. For example, people inquire and print a bill list through a self-service terminal device in a Telecom business office, and deposit and withdraw money, and print a transaction voucher through a self-service terminal device in a self-service kiosk of a bank. Generally, a self-service terminal device uses continuous paper to print a voucher. The continuous paper is wound on a paper tube to form a paper roll. The continuous paper is cut off by a cutting device each time when printing is finished, so as to form a single voucher which is delivered to a user. When the paper roll is used up, the self-service terminal device sends out prompt information to prompt a service staff member to replace the paper roll. Usually, a paper roll having a large external diameter, such as a paper roll having an external diameter of 200 mm to 250 mm, is used in order to reduce a frequency of changing paper rolls and reduce labor cost. When printing begins, the load of a motor dragging the static paper roll which is relatively heavy with a relatively large external diameter to move is maximized under the effect of inertia, thus easily resulting in a problem that printing content is compressed due to the incapability of the motor to drag the paper roll.
A buffer mechanism is arranged between the paper roll and a printing device in the prior art in order to solve the foregoing problem. As shown in FIG. 1, the buffer mechanism 17′ is arranged between a paper roll supporting frame 13′ and the printing device. The buffer mechanism 17′ includes a swing arm 71′, a buffer shaft 73′ and an elastic element 74′ and two transition rollers 16′, wherein one end of the swing arm 71′ is pivoted with a frame (not shown in the figure) through a pivoting shaft 72′ and is capable of swinging around the pivoting shaft 72′. The buffering shaft 73′ is arranged on a free end of the swing arm 71′. One end of the elastic element 74′ is connected with the frame and another end is connected with the swing arm 71′. The two transition rollers 16′ are located upstream and downstream the buffer shaft 73′ respectively along a conveying direction of continuous paper. The continuous paper 24′ is draw from by a paper roll 7′ to pass through a location below the buffer shaft 73′ after passing through a location above the transition roller 16′ upstream the buffer shaft 73′, and then enter into a location between a printing head 12′ and a platen 11′ after passing through a location above the transition roller 16′ downstream the buffer shaft 73′. At the moment, the swing arm 71′ rotates around the pivoting shaft 72′ under the action of the elastic element 74 and the continuous paper 24′ is always tensioned by the buffer shaft 73′ located on the swing arm 71′. In this way, the buffer shaft 73′ can provide buffer to reduce the load of a motor when the motor is started and accelerated after printing begins, thus avoiding the problem that printing content is compressed.
Such buffer mechanism has a problem that a user may place the continuous paper between the printing head 12′ and the platen 11′ directly by mistake without passing through the buffer shaft 73′ when loading the paper, thus the load of the motor cannot be reduced, and the printing content cannot be prevented from being compressed.